Recently, the general trends in designing computers and their peripheral devices are toward small size, light weightiness and easy portability. Take keyboards for example. The manufacturers of the keyboards are devoted to the study of designing slim keyboards in order to minimize the size thereof. In addition, the demands on enhancing comfort of the key structure and properly controlling the depressing force are gradually increased.
Nowadays, the slim keyboard used in for example a notebook computer usually has a scissors-type support member for support the key structure. FIG. 1 is a schematic cross-sectional view illustrating a key structure with a scissors-type support member according to the prior art. As shown in FIG. 1, the key structure comprises a keycap 71, a rubbery elastomeric element 72, a scissors-type support member 60 and a base plate 74. The scissors-type support member 60 comprises inner support arms 61 and outer support arms 62. A lever structure with fulcrums is formed between the inner support arms 61 and the outer support arms 62. By the upper fixing parts 75 of the keycap 71 and the lower fixing parts 76 of the base plate 74, the scissors-type support member 60 is pivotally fixed between the keycap 71 and the base plate 74. In a case that a downward force is exerted on the keycap 71, the keycap 71 is moved downwardly in the vertical direction under the guiding action of the scissors-type support member 60. As such, the rubbery elastomeric element 72 is pressed and subject to deformation. In a case that the downward force exerted on the keycap 71 is eliminated, an elastic restoring force is provided by the rubbery elastomeric element 72. Due to the elastic restoring force, the keycap 71 is returned to its original position. Since the key structure with the scissors-type support member has many pivotal parts, the upper fixing parts 75 and the lower fixing parts 76, the process of assembling the key structure is very troublesome. In addition, since the components of the key structure are complicated and diversified, the fabricating cost of the key structure is very high. The scissors-type support member 60 is operated according the principle of leverage. Due to the limitations of the plastic molding technology, the lever fulcrums and the lever arms (e.g. the inner support arms 61 and the outer support arms 62) of the scissors-type support member 60 become hindrance from reducing the overall height of the key structure. In other words, when the key structure with the scissors-type support member is used in a notebook computer, the notebook computer fails to meet the requirements of small size, light weightiness and easy portability small size, light weightiness and easy portability.